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Chapter 22.

Evidence of Evolutionby Natural Selection

Dodo bird

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Evolution is "so overwhelmingly established that it has become irrational to call it a theory."

-- Ernst Mayr What Evolution Is

2001Professor Emeritus, Evolutionary Biology

Harvard University

(1904-2005)

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Support for Darwin’s ideas Fossil record

change over time Biogeography

related organisms in similar range

Comparative anatomy Comparative embryology Molecular biology

measure of common ancestry

Artificial selection induced evolution

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Fossil record Layers of sedimentary rock contain fossils

new layers cover older ones, creating a record over time

fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

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Fossil Record

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Fossil record Today’s organisms descended from

ancestral species

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ArchaeopteryxFossil of Archaeopteryx, reptilian bird ancestor that lived about 150 million years ago.

Smithsonian Museum, Washington, DC

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??

??Where are the

Intermediates?

Land Mammal

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Study of Paleontology

Georges Cuvier (1769-1832)

Older sediments are below younger sediments.

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Gradualism James Hutton (1726-1797)

Earth’s geologic features — profound change formed as product of slow but continuous & cumulative processes

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UniformitarianismCharles Lyell

(1797-1875)geologic processes

have not changed throughout Earth’s history

Conclusion: Earth must be much older than 6,000 years

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Biogeography Geographical distribution of species

species living in the same region tend to be more closely related to each other

species which look similar but are from different regions are often not closely related

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Biogeography Convergent evolution

evolving similar solutions to similar “problems”

marsupial mammals

vs.

placental mammals

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Analogous structures

Convergent evolution of structures similar functions similar external form different internal structure &

development different origin no evolutionary relationship

Solving a similar problem with a similar solution

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Analogous structures Dolphins: aquatic mammal Fish: aquatic vertebrate

have adapted to life in the sea

not closely related

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Analogous structures 3 groups with wings

does this mean they have a recent common ancestor?

flight evolved 3 separate times = evolving similar solutions to similar “problems”

flight evolved 3 separate times = evolving similar solutions to similar “problems”

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Homologous structures Homology

similarities in characteristics resulting from common ancestry

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Homologous structures Forelimbs of human, cats, whales, & bats

share same skeletal structures similar structure similar embryological development different functions evidence of common ancestor

branched off from common 4-limbed ancestor

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Homologous structures Similar structure Similar development Different functions Evidence of a recent

common ancestor

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Vestigial organs Modern animals may have structures

that serve little or no function remnants of structures that were

functional in ancestral species evidence of change over time

some snakes & whales show remains of the pelvis & leg bones of walking ancestors

eyes on blind cave fish

human tail bone

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Vestigial organs Hind leg bones on whale fossils

Why would whales have pelvis & leg bones if they were always sea creatures?

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Comparative embryology Similar embryological development in

closely related species all vertebrate embryos have a gill pouch

at one stage of development fish, frog, snake, birds, human, etc.

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Molecular biology Comparing DNA & protein structure

universal genetic code! DNA & RNA

cytochrome C (respiration) protein structure

hemoglobin (gas exchange) protein structure

Evolutionary relationships among species are documented in their DNA & proteins.Closely related species have sequences that are more similar than distantly related species.

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Comparative hemoglobin structure

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Building “family” treesClosely related species (twigs of tree) share same line of descent until their recent divergence from a common ancestor

What data from whole genome sequencing can tell us about evolution of humans

What data from whole genome sequencing can tell us about evolution of humans

Example: the Evolutionary Hypothesis

of Common Ancestry

Chromosome Numbers in the great apes:

human (Homo) 4646chimpanzee (Pan) 48gorilla (Gorilla) 48orangutan (Pogo) 48

Testable prediction:Testable prediction: If these organisms share a common ancestor, that ancestor had either 48 chromosomes (24 pairs) or 46 (23 pairs).

Testable prediction:Testable prediction: If these organisms share a common ancestor, that ancestor had either 48 chromosomes (24 pairs) or 46 (23 pairs).

Chromosome Numbers in the great apes (Hominidae):

human (Homo) 46chimpanzee (Pan) 48gorilla (Gorilla) 48orangutan (Pogo) 48

Testable prediction:Testable prediction: Common ancestor had 48 chromosomes (24 pairs) and humans carry a fused chromosome; or ancestor had 23 pairs, and apes carry a split chromosome.

Centromere

Telomere

Ancestral Chromosomes

FusionHomo sapiens

Inactivated centromere

Telomere sequences

“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two acrocentric chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1 (ref. 2; hg 16:114455823 – 114455838), where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22 (Fig. 3; Supplementary Fig. 3a, region A). During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated (42).”

“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two acrocentric chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1 (ref. 2; hg 16:114455823 – 114455838), where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22 (Fig. 3; Supplementary Fig. 3a, region A). During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated (42).”

Homo sapiens

Inactivated centromere

Telomere sequences

Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.

Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.

Human Chromosome #2 shows the exact point at which this fusion took place

Human Chromosome #2 shows the exact point at which this fusion took place

Chr 2

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Artificial selection Artificial breeding can use differences

between individuals to create vastly different “breeds” & “varieties”

“descendants” of the wolf

“descendants” of wild mustard

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Natural selection in action Insecticide &

drug resistance insecticide didn’t

kill all individuals resistant survivors

reproduce resistance is

inherited insecticide

becomes less & less effective

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Evolution of DrosophilaAll of the 500+ endemic species of Drosophila in Hawaiian archipelago descended from common ancestor that reached Kauai over 5 million years ago

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Witness to Evolution Peppered Moth

dark vs. light variants

Peppered moth

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Peppered moth

Year % dark % light1848 5 951895 98 21995 19 81

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Peppered moth Why did the population change?

early 1800s = pre-industrial England low pollution lichen growing on trees = light colored bark

late 1800s = industrial England factories = soot coated trees killed lichen = dark colored bark

mid 1900s = pollution controls clean air laws return of lichen = light colored bark

industrial melanism

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Unity & Diversity Only evolution explains both the unity

& diversity of life By attributing the diversity of life to

natural causes rather than to supernatural creation, Darwin gave biology a strong, scientific, testablefoundation